1. Field of the Invention
This invention relates generally to elastomer compositions having carbon black and more particularly, to elastomer compositions useful for tires and their components.
2. Description of the Related Art
Carbon blacks are widely used as pigments, fillers and reinforcing agents in the compounding and preparation of rubber and other elastomeric compounds. These materials are particularly useful as reinforcing agents in the preparation of elastomeric compounds used in the manufacture of tires.
A furnace-type reactor produces carbon black by pyrolyzing a hydrocarbon feedstock with hot combustion gases. The pyrolysis combustion products include particulate aggregates of carbon black particles. Carbon blacks are generally characterized on the basis of their physical characteristics, including, but not limited to, particle size and specific surface area; aggregate size, shape and distribution; and chemical and physical properties of the surface.
Carbon blacks are classified according to a standard classification system provided under ASTM designation D1765. In accordance with this standard, rubber grade carbon blacks are classified using a four-character nomenclature: the first character gives an indication of the influence of the carbon black on the rate of cure of a typical rubber compound containing the carbon black; the second character, the group number, gives information on the average surface area of the carbon black and the last two characters are assigned arbitrarily. Thus, for example, an N347 carbon back describes, with the “N,” a carbon black that has a normal effect on the cure rate and, with the group number “3,” indicates a carbon black having an average nitrogen surface area of between 70 and 99 m2/g.
In the manufacture of tires, carbon blacks are selected for use in the tires based upon the preferred characteristics of the rubber mix. For example, a truck tire tread may be manufactured from a rubber mix containing a carbon black having the physical properties of a rubber black assigned to the N200 classification series. By contrast, the carcass of the tire may be manufactured from a rubber mix containing a carbon black having the physical properties of the N600 carbon black classification series. Such selections are made based upon the known effects that different classes of carbon black have on the physical properties of the rubber such as, for example, the hysteresis and rigidity of the mix.
Carbon black is not the sole reinforcing agent or filler that may be used in a tire manufacturing elastomer compound. For example, silica may be added to an elastomer compound to replace some or all of the carbon black and thereby enhance certain performance characteristics. The use of silica as a reinforcing agent in the elastomer mix does, however, have some drawbacks in that the resulting elastomer compound may exhibit low thermal conductivity, high electrical resistivity, high density and poor processability.